1. Field of the Invention
The present invention relates generally to a method and apparatus for recognizing different types of batteries, and more particularly to a method and apparatus for recognizing different types of batteries to efficiently employ the available power in a battery.
2. Description of Related Art
Batteries are typically used to supply power to portable products such as radios, radiophones, stereo cassette tape players, etc. A Ni--Cd battery is a type of battery that is rechargeable and that has a discharge voltage that drops rapidly at a certain point. An alkaline battery is a type of battery that is not rechargeable but has a discharge voltage that drops gradually to the end of its useful life.
FIG. 1 is a graph showing discharge characteristics of the Ni--Cd battery and the alkaline battery, and showing monitored voltages Va and Vb. In FIG. 1, the available voltage of battery is referred to as Va. In some products, when the battery voltage drops under the available voltage Va, a microprocessor generates an alarm signal, through a buzzer, LCD etc., indicating that the battery should be charged or exchanged.
In FIG. 1, a cut-off voltage for shutting the system down is referred to as Vb. When the battery voltage drops under the cut-off voltage Vb, a microprocessor shuts down system operation.
In FIG. 1, the time to reach the Va of Ni--Cd is referred to as tNi1 and the time to reach the Vb as tNi2. When using Ni--Cd battery, because the time between tNi1 and tNi2 is relatively short, the battery should be promptly recharged or exchanged to prevent the battery voltage from falling below the cut-off voltage Vb.
If a battery such as an alkaline battery were to be used with monitored voltages set for a Ni--Cd battery, the use time of the alkaline battery may be unduly restricted. More specifically, the time to reach the available voltage Va of the alkaline battery is referred to as tAL1 and the time to reach the cut-off voltage Vb as tAL2. Since the discharge characteristics of the alkaline battery is long and linear, the time between tAL1 and tAL2 is several times as long as the time between tNi1 and tNi2 of a Ni--Cd battery, as shown in FIG. 1. Thus, when an alkaline battery is removed in accordance with an alarm signal generated based on Ni--Cd battery monitored voltages, there may be available power in the alkaline battery that is not used.
Therefore, in products using the two types of batteries, for example, a Ni--Cd battery or an alkaline battery, there is a problem that the available power of the alkaline battery is not sufficiently used. Alternatively, if monitored voltages are set to accommodate an alkaline battery, there is a possibility that erroneous operations of the electrical circuits can occur when using the Ni--Cd battery.